Structure and Function of the Central Nervous System – Biological Bases of Behavior (PSY, BIO)

The human nervous system weighs “only” about 4.5 pounds, which accounts for approximately 3% of the entire body. It is a small and complex body system that consists of an intricate network of nervous cells (or neurons) and even more glial cells. How many nervous cells does a human have? Billions, is the simple answer. However, from a medical point of view, the more important questions are: how does the nervous system work, and what does its structure look like?

00:02
Okay. Now let’s move to our counterpart,
which is the central nervous system.
00:05
So like I said, it’s made up of
the spinal cord and the brain.
00:08
The brain has three main subdivisions,
the hindbrain, midbrain, and forebrain.
00:13
So there are also the older
names that have been used,the rhombencephalon, the
mesencephalon, and prosencephalon.
00:18
You should probably
know those for the MCATbecause they might not refer
to them as hindbrain.
00:22
They most probably will, but they might
also throw around these other name,so you should kind of associate
which one goes with which.
00:29
The entire CNS is
contained within this sacand it’s bathed in this solution
called the cerebrospinal fluid or CSFand it’s basically a salt
solution so it’s saline.
00:40
We say it’s a circulating
saline solutionwhich provides all the different
nutrients, protection, and removes waste.
00:46
So nutrients make sense
because it’s bathed in stuffand it has all the ions, the sodium,
the potassium, the calcium,and all those things that it needs.
00:52
And it provides protection because the brain
actually sits floating inside the skull,inside different layers of membrane
and this cerebrospinal fluid.
01:06
So the analogy I like to use is think
of maybe a large container of soupor something like a metal tinand if inside that you
put a water balloonand then you fill that up with a little
bit of water and put the lid back on.
01:21
So that would sort of
represent the skull and brainwith the outside of that
hard tin being the skull,then you have your brain
which is the water balloon,and then you have water and that
kind of allows it to float around.
01:31
And you want that because
if there was not CSF,you would have your very tender,
soft, malleable brain tissueagainst this rigid, hard skulland just walking
around or dancing,you basically would be causing major brain
trauma, which you don’t want to be doing.
01:48
So by having this kind of floating system,it allows it that buffer
and that ability todeal with a lot of the movement
and impact that we deal with.
01:59
Here’s the basic structure,
again, not a lot of components.
02:02
We have the brain, we have the spinal
cord, and then we have everything else,which is the peripheral nervous
system, we have the ganglion cells,and we have all the nerves that exit the
spine going to all the different effectorsand getting sensory information as well
that goes up to the spinal cord --up through the spinal cord to
the central nervous system.
02:19
So easy divide. Brain, spinal cord,
CNS; everything else is PNS.
02:26
Here’s a nice blowup
of the spinal cord.
02:28
It shows that it’s actually a
stacking of different bone segmentsand each one is separated by
some tissue and cartilageand there’s a cavity that allows these nerves
to go in and to go up to the spinal cord.
02:43
So it’s connected to the brain and
is protected by the CSF as well,so it also has the same fluid
and has a vertebral column.
02:52
This is the pathway for sensory
data to go to the brainand it allows for integration
and processing up at the brain.
02:59
There’s some integration and processing that
actually happens in the spinal cord too.
03:03
So as things come
in, they synapse,and you’re starting to see some
integration happen right on the spot.
03:09
And it’s also responsible for
simplest spinal reflexeslike the muscle stretch
reflex which we talked about.
03:14
So it prevents it from having to
go all the way up to the brain.
03:16
It can happen right there at the synapses
happening within the spinal cord.
03:23
Now let’s take a look at
some of the structures ineach of those different
regions that we talked about.
03:27
We’ll start with the hindbrain.
03:28
So first off you have
the medulla oblongata.
03:30
This is a spot that relays information
between the different areas of the brain.
03:35
So it’s sort of like a major hub.
03:38
It regulates vital
autonomic functionsincluding blood pressure,
digestive function, vomiting.
03:44
So again, these are things that you might
not necessarily be thinking about.
03:47
And kind of a simple rule
of thumb that we havefor the brain is the deeper
you are in the brain,sort of the more rudimentary
or simple the function,and as you peel that onion
and you go on the outside --actually, not peel the onion, but add
layers to the onion and move farther away,the more sort of complex and
higher level the function is.
04:08
So the very -- the base of the
brain being simple stuff,and the very outside or the
cortical layers is where we doa lot of our executive function
and higher level thinking.
04:17
So the pons is a connection point between
the brainstem and the cerebellumand this coordinates
movement and balance.
04:23
So we’re not going to spend tons of
time going through each of thesebecause simply put you need
to know these structuresand you need to know their
basic function for the exam.
04:32
The cerebellum is also
known as little brainand sort of basically because of
its function and its location.
04:40
So we say it’s an integrating center
where complex movements are coordinated.
04:45
The midbrain now is a relay for
visual and auditory information.
04:51
So this is where a lot of
that input is now coming in.
04:53
And it also contains the RAS, which
has come up at other lecturesas the reticular activating system, which
is responsible for arousal and wakefulness.
05:01
And the link I always tell people
if you don’t remember thinkof arousal or being activatedand this is called the reticular
activating system or RAS.
05:11
The brainstem refers to the midbrain
along with the medulla and pons.
05:15
So you’ll also hear
that term brainstem,I mean I myself have
been using it alreadyand that’s what we’re referring
to actually, is the midbrainand the medulla and the pons.
05:24
Now the forebrain includes the
diencephalon and telencephalon.
05:28
And the diencephalon includes structures
like the thalamus and the hypothalamus.
05:33
The thalamus contains relay and processing
centers for sensory information,and the hypothalamus contains
centers for controlling emotions,autonomic functions, and a major role
in hormone production and release.
05:43
So quite a bit of stuff they’re doing,
this is kind of advanced stuff,so now layering an emotion and
processing actual sensory information.
05:51
This is sort of higher level stuff.
05:55
Here’s a nice image looking at
all the different componentsof the central nervous
system as a wholeand there’s a few that
I want to highlight.
06:05
One, the locations of the structures
that we’ve already talked about,so the hypothalamus, the midbrain,
the cerebellum, the brainstem.
06:13
I want you to also notice how
the spinal cord comes upand then is connected to the brainstem and
it’s kind of at the base of the brain.
06:21
And we have something
called the corpus callosum.
06:24
Corpus callosum, this
is also very important.
06:26
And this is a bundle of fibers that
connects the two hemispheres of the brain.
06:33
So we haven’t gotten there yet, but basically
the brain is made up of two halves.
06:36
I’m sure you’ve heard of that
before, left brain, right brain,but there’s actually a physical clear
marcation between the two sides of the brain.
06:46
The two hemispheres are connected,one of the connections is
through this corpus callosum.
06:51
So here’s an image looking at, you
know, an animal model of the brainand you can see as you
spread the hemispheres apart,you can clearly see
the corpus callosum.
07:02
So it connects the two
cerebral hemispheres.
07:05
In this diagram you also can see the
location of the cerebellum, as well.
07:12
Now the two sides have some differences.
07:15
So generally speaking, both
hemispheres have similar functions,but there’s a little bit of
differentiation in each.
07:21
So for example, at the rear of
the brain at the occipital lobe,we know that that lobe is primarily
dealing with visual function.
07:29
Now, the left and right side of the occipital
love both deal with visual function,but they might control and modulate and
mediate different aspects of vision.
07:38
So the hemispheres are bilateral,
meaning two sides, left and right.
07:43
The left side of the brain controls
the motor function of the right side,and the opposite holds true.
07:49
So when I’m moving right hand I’m
actually using the left side of my brain,and when I’m using my left hand I’m
using the right side of my brain.
07:56
So information is crossed.
07:59
The left hemisphere is generally
responsible for speech,while the right hemisphere is responsible
for visual-spatial reasoningand for interacting with things like music,a little bit more of the artsy side, okay?So here are the lobes,
you’ve seen these before.
08:15
You should be very familiar with
their location and their names.
08:19
So the frontal lobe,
top of the hat,it’s nice to meet you and
you’ll remember thatbecause it’s at the front
of your brain, okay?Then we have the occipital lobe
which is at the back of the brainand this is the part of the brain
that deals with visual function.
08:32
And then we have the parietal lobe
which is kind of in between the two.
08:35
And then the temporal lobe if you want to
remember is where your temples are, okay?So you should know their locations.
08:41
Now the frontal lobe initiates
all voluntary movement,complex reasoning, problem solving.
08:47
So the prefrontal cortex,
the frontal lobe,these are all areas that kind of
do that higher level thinking,deal with emotion, help
shape your behavior.
08:54
The parietal lobe is involved in general
sensation and taste, gustation,so it’s more around
sensory functionand this is also where we have the
somatosensory cortex and the homunculuswhich we’ve talked about in
some of the other lectures.
09:10
The temporal lobe processes
auditory and olfactory sensationand it deals with short-term
memory, language, comprehension,and is also involved
in emotions.
09:18
So you can see that certain
parts of your brain are verylocalized and focused
on a specific functionand now they’re a little bit more
diverse and do quite a few things.
09:27
Occipital lobe, an
example of being prettyfocused in dealing with
just visual information.
09:34
Now, how do you study the brain?Well, there’s a lot of ways of doing it.
09:38
So you can have two broad categories.
09:42
Invasive is when you’re actually
going and poking and prodding,there’s noninvasive where you’re
looking at usually a more behavioralor indirect measures and we’re
also looking at in today’s worldsome of the cool bio-imaging
that we now haveand you’re not drilling holes
and opening up the skull.
10:00
So you can also have the scenario of
some of this being behind damage, right?So you can look at the effect
of brain damage or injuryand this is what we call
a natural experimentbecause hopefully you’ll
have some information beforeor you might have normal function,and then you have some type of
injury, a stroke or trauma,and then you can look at
what’s happened post-trauma.
10:21
How was this changed?Look at the changes in behavior,
psychological changes,and you can look at
functional changes, as well.
10:28
You can also have, say, maybe postop if
it was a significant trauma like death,you could look at a biopsy data,where you’re looking at
histological and pathological data,so looking at cross-sections of brain,
staining, looking under a microscope,and looking at “Oh, I’m seeing this.”So again, you’re looking
hands on at what’s happened.
10:48
You can have a look at
chemical/electrical stimulationlooking at actual psychotropic
or brain-changing agents.
10:56
You can look at ECT, which is
electroconvulsive therapy.
11:00
You can look at conduction
stimulation looking at electrodes.
11:04
You can look at different animal models.
11:07
This is really the bulk of where a
lot of medical research is done.
11:11
We can have chemical/electrical
simulation through EEGand the example that we used
was looking at recordingsfrom when you’re looking at
different stages of sleepand they were capturing electrical activity
and it allows us to understand function.
11:24
And then more recently and
much more cool is bio-imaging.
11:29
So things like CT scans, PET scans,MRIs which uses magnets,
magnetic resonance imaging,and we have a lot of really
new cool hybrid techniquesto image the brain
without having to go inand they can do that at
such higher resolutionthat can go down right down
to the cellular level.
11:48
And they can look at presence of
anomalies like tumors or growths.
11:54
We can look at internal bleeding.
11:56
We can look at so a stroke.
11:58
We can look at a function,
changes in glucose utilization.
12:02
So how active is that area of the brain,really, really cool stuff in order to study
the brain and understand its function.
12:09
So let’s take a look at the
influence of neurotransmittersand how they impact behavior.
12:13
So we’ve explained what a neurotransmitter
is, we’ve explained the process of release.
12:18
Now we’re going to look at the
different neurotransmittersand what impact they actually
have on our behavior.
12:24
So transmitter release and the
impact that they have on behaviorcan be attributed to three things
that we want to talk about right now.
12:32
So one is genetics, the
second is lifestyle,and the third is injury or disease.
12:37
Let’s start with acetylcholine.
12:39
It is involved with voluntary
movement, memory, learning, and sleepand we know that we have elevated
levels in certain individualsthat are expressing depression, and we
also have low levels can cause depression.
12:50
So this is one that has kind of a lot of
range and does a lot of different things.
12:55
Dopamine is really, really popular
when we’re looking at behavior.
12:58
So it is a happy transmitter.
13:01
Excuse me.
13:02
It causes feelings of pleasure,it can help modulate voluntary movement,
it’s associated with learning.
13:09
And what it does is it actually
activates the reward area,an area within the limbic system
called the dopamine reward pathway.
13:15
And we know that if you are doing
something that’s positively reinforcing,so a good behavior, you see
a release in dopamine.
13:23
If you happen to maybe snort some
cocaine or take some heroine,that also causes a change in levels
of dopamine in the reward pathwaymaking that a behaviorally
reinforcing actionso you want to continue to do that
positively reinforcing behavior.
13:37
And some examples in terms of inappropriate
levels and the effect on behavior,we can have schizophrenia, Parkinson’s,
disorders that we’ve mentioned,and that’s linked to inappropriate
levels of dopamine.
13:50
Norepinephrine causes arousal, alertness,and may stimulate the
sympathetic nervous system.
13:54
So we know lower levels
can cause depressionand it can be linked to changes
in terms of stress hormones.
14:01
So serotonin is the last one
that we want to mention hereand directly linked to anxiety
disorders, depression,and it’s typically regulating things
like appetite, sex drive, and mood.
14:11
So what we’re trying to
show here is a clear linkbetween a transmitter
and the behavior.
14:17
So there is obviously a lot
of impact that you can haveif you’re changing the levels
of this neurotransmitter,whether it’s a through pharmacotherapy,
taking medicine, using recreational drugs,or even things like changing your
diet can have a dramatic impactin the levels of neurotransmitter
and the ultimate behavioral effect.

About the Lecture

The lecture Structure and Function of the Central Nervous System – Biological Bases of Behavior (PSY, BIO) by Tarry Ahuja, MD is from the course Individual Influences on Behavior.

Included Quiz Questions

Which structure is part of the rhombencephalon?

Medulla

Frontal lobe

Parietal lobe

Temporal lobe

Hippocampus

What is the mesencephalon?

Midbrain

Forebrain

Hindbrain

Afterbrain

Spinal cord

Which area of the brain is responsible for autonomic functions?

Hindbrain

Telencephalon

Sympathetic ganglia

Prosencephalon

Spinal cord

Which area of the brain is responsible for the sleep-wake cycle and arousal?

Mesencephalon

Telencephalon

Metencephalon

Myelencephalon

Brainstem

A 5-year-old child is diagnosed with a medical condition that causes a deficiency in thyroid and growth hormones. Investigations show an abnormal hypothalamus caused by a developmental malformation. Which other structure might be affected?

Thalamus

Medulla

Pons

Corpus callosum

Basal ganglia

A 72-year-old man had a stroke 3 months ago. Since then, he has experienced decreased motor ability and sensory perception on the right half of his body. What structure(s) might have been injured?

Left hemisphere

Cervical spinal cord injury

Right hemisphere

Brainstem

Corpus callosum

Researchers have observed that when subjects are asked to read a book, describe intense emotional moments or learn a foreign language, one particular area of the brain lights up. What area is this?

Temporal lobe

Right frontal lobe

Cerebellum

Left occipital lobe

Parietal lobe

Autopsy of a patient's brain shows a growth in the right parietal lobe. How would the patient have been affected ante-mortem?

Altered perception of sensory information

Difficulty with speech

Difficulty with comprehension

Decreased vision in upper quadrant of visual field

Altered emotional comprehension and planning

What change in neurotransmitters might be observed in a patient with depression?

Increased acetylcholine

Increased norepinephrine

Increased serotonin

Decreased glutamate

Decreased dopamine

What neurochemical changes would be observed in a patient with panic attacks and anxiety?

Decreased serotonin

Decreased norepinephrine

Decreased dopamine

Decreased acetylcholine

Increased acetylcholine

Author of lecture Structure and Function of the Central Nervous System – Biological Bases of Behavior (PSY, BIO)

Tarry Ahuja, MD

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